For the first part, take x,a,ϵ>0, and note that
|x−−√−a−−√|≥ϵ⇒|x−−√−a−−√|≥ϵa−−√a−−√⇒|x−−√−a−−√|≥ϵa−−√x−−√+a−−√⇒|(x−−√−a−−√)(x−−√+a−−√)|≥ϵa−−√⇒|x−a|≥ϵa−−√.
Hence, for any
ϵ>0, defining
δ=ϵa−−√, we have
Pr(|Xn−−−√−a−−√|≥ϵ)≤Pr(|Xn−a|≥δ)→0,
when
n→∞, implying that
Xn−−−√→Pra−−√.
For the second part, take again x,a,ϵ>0, and cheat from Hubber's answer (this is the key step ;-) to define
δ=min{aϵ1+ϵ,aϵ1−ϵ}.
Now,
|x−a|<δ⇒a−δ<x<a+δ⇒a−aϵ1+ϵ<x<a+aϵ1−ϵ⇒a1+ϵ<x<a1−ϵ⇒1−ϵ<ax<1+ϵ⇒∣∣ax−1∣∣<ϵ.
The
contrapositive of this statement is
∣∣ax−1∣∣≥ϵ⇒|x−a|≥δ.
Therefore,
Pr(∣∣∣aXn−1∣∣∣≥ϵ)≤Pr(|Xn−a|≥δ)→0,
when
n→∞, implying that
aXn→Pr1.
Note: both items are consequences of a more general result. First of all remember this Lemma: Xn→PrX if and only if for any subsequence {ni}⊂N there is a subsequence {nij}⊂{ni} such that Xnij→X almost surely when j→∞. Also, remember from Real Analysis that g:A→R is continuous at a limit point x of A if and only if for every sequence {xn} in A it holds that xn→x implies g(xn)→g(x). Hence, if g is continuous and Xn→X almost surely, then
Pr(limn→∞g(Xn)=g(X))≥Pr(limx→∞Xn=X)=1,
and it follows that
g(Xn)→g(X) almost surely. Moreover,
g being continuous and
Xn→PrX, if we pick any subsequence
{ni}⊂N, then, using the Lemma, there is a subsequence
{nij}⊂{ni} such that
Xnij→X almost surely when
j→∞. But then, as we have seen, it follows that
g(Xnij)→g(X) almost surely when
j→∞. Since this argument holds for every subsequence
{ni}⊂N, using the Lemma in the other direction, we conclude that
g(Xn)→Prg(X). Hence, to answer your question you can just define continuous functions
g(x)=x−−√ and
h(x)=a/x, for
x>0, and apply this result.